The long-term goal is to gain insight into the mechanisms regulating nerve growth factor (NGF) synthesis in Schwann cells and the function of their NGF receptors. The immediate objectives are to establish that these cells synthesize NGF and to examine the properties of their NGF receptors. In the first specific aim, the amount of an NGF-like material will be measured by a two-site enzyme immunoassay, its molecular characteristics identified by protein radiolabelling and gel electrophoresis and its biological activity assessed by a standard in vitro assay that uses NGF-dependent neurons. A cDNA probe to detect messenger RNA for NGF should determine if these cells actually synthesize the factor. The second specific aim is to characterize the NGF receptors on Schwann cells since they may play a role in controlling the extracellular NGF concentration. Standard ligand-receptor binding assays using iodinated NGF will be performed in monolayer cultures. These experiments provide information about the concentration of receptors, the number of receptor subtypes with their respective affinities and dissociation rates, the relative amounts of receptor within internal and external pools, and their capacity to internalize the NGF protein. The last specific aim of this project will focus on several factors that may regulate the synthesis of NGF or properties of the NGF receptor. These include the state of the Schwann cell, i.e., "resting" (induced by a mitotic inhibitor), "dividing"(induced by a mitogen) and "differentiated" (induced by axonal membranes) and the external NGF concentration. The amount of NGF protein and its messenger RNA as well as the kinetics of the NGF receptor will be examined under these conditions. By studying the regulations of NGF synthesis by Schwann cells and the role of their NGF receptors in vitro, we ultimately hope to gain a better understanding of not only how neurotrophic factors secreted by Schwann cells function during regeneration but how these factors could be used to aid the process.